The Power System


Power Converter (images show Datel)

  1. The Datel UWR-5/3000-D5 converter converts 4.5 to 13.2V DC into the 5V DC the PC/104 boards expect. See the specs that come with it for exact information.

    Note again, a higher voltage version might be preferrable,

  2. Find the PC/104 power connector from the Ampro kit.

    Allign the PC/104 power connector as shown below. Note that the connector is "keyed" (i.e. one pin hole is blocked so that it can be attached only one way).

    Remove all the leads except for the two leftmost (red and black: positive and negative). The leads can be removed from the small connector by simply pressing on the indicated spot and pulling.

    Cut off the large connector, and strip the extraneous wires so that it looks like this:

  3. Attach the PC/104 power connector to the output side of the DC to DC converter. Note: to make the most stable connection, wrap the wire around the pin of the converter, bend down the pin of the converter, and solder in place.


  4. Attach a fuse holder to the positive pin on the input side of the DC converter. Insert fuse (about 10A).
  5. Attach about 3 feet of stranded wire (preferably red and black 18 gauge) to the input side of the DC to DC converter. Note that the fuse holder replaces a section of the (positive) red wire. The result should look like

  6. If you wish NOT to have an isolated converter, connect the negative pins to each other as shown here. Isolated converters are convenient for those doing medical experiments (due to regulations) or those who plan to plug their wearable into something besides batteries.

  7. Attach male banana jacks (red and black) to the end of the wires. Here's how to use the Radio Shack jacks we use

  8. Test the converter by plugging it into a battery and testing the output (should be 5V DC).
  9. Place a layer of cardboard on top of the connections for insulation, and use (preferably black) duct tape to hold it in place. Keep the front of the converter clear since it will get hot. Insulate any remaining exposed wire with the tape.

Making the computer

Installing Software

Install the hard disk using the small IDE cable provided in the kit. One end of the cable

goes to the CPU board, the other to the hard drive. The cable is keyed, and the position of the connector on the cable does not matter. Power to the drive is provided through the cable.

The next step really depends on what you want to do, which OS you intend to run, and what you have available. I suggest starting the case instructions while waiting for software to install.


For most folks, attaching hard and floppy drives as in

and going through a floppy install of the OS is the easiest way to install software. Note that the hard drive installs on the back of the CPU board and the floppy on the left side (where the screwdriver points). Other methods include buying a IDE CD-ROM and installing it on the second connection on the IDE cable. To do this, a small to big IDE cable adapter kit is necessary. Toshiba makes something called the HD002KU2.5 - Install kit for 2.5" HDD which should do the trick, and a standard PC power supply is needed to provide external power to the CD-ROM (can be picked up at any computer store). Yet another option is to plug the wearable into the net with a Dlink, boot Linux from a floppy, and download the OS from the net. Other options include downloading the OS over a serial port, hooking up the 2.5 inch drive into another machine, or programming the OS into flash (optional on the Ampro boards).

At the lab we use (and highly recommend) Linux (we are currently using the 2.0.21 kernal). A good beginning book on the subject is Using Linux published by Que. Shows how to install the software and perform many configurations.

We provide drivers for X for the Private Eye, Twiddler keyboard, and Sierra Wireless modems on the main pages. Most everything else is probably already written with source provided on web sites or in standard Linux distributions (Slackware, Red Hat, Debian, etc.). In my personal experience, Linux, even though public domain, tends to provide better supported than what Microsoft can provide - its just a matter of knowing where to look. In the worst case, it's usually easy to write new device drivers in Linux.

For those who insist on Microsoft Windows, I believe drivers exist for most of the equipment we use. However, they tend to be less flexible and robust. If using DOS, be aware that battery life may be halved compared to Linux. This rather fantastic result is supported by precise testing. The current theory is that the powersaving 486/586's used in the CPU boards execute low-power "hlt" instructions in Linux's idle loop while DOS is doing something else. Have not compared to Windows.


And folks who have a friend with a disk with software already installed (assumes linux and that the same model hard disks are being used), the following procedure will make a copy of the disk.

  1. Let's call the hard disk with software installed the "master" and the one without data the "slave."
  2. Jumper the slave to be the second (slave) hard drive. For the Toshiba 2.5" drives this is as shown:

  3. Plug both the master and the slave disks into the IDE cable. Make sure the circuit board on the drives can not short into anything.
  4. Boot Linux.
  5. Type "dd if=/dev/hda of=/dev/hdb bs=18k"
  6. After a long while, the copy will finish.
  7. Take both drives off, unjumper the slave, reattach the slave, and make sure it boots.

Preparing the case

  1. Unscrew the case screws about 1 turn. The case should slide apart easily.
  2. Place the edge of the case on a desk. Use a screwdriver to work the punchouts on the IO panel back and forth until they come out.

  3. Attach the serial and parallel ports to the case (use the hex nuts so that devices can be secured to the ports).

Putting it together.

IMPORTANT: Follow the instuctions below to lay out the components once before doing it for real. This will forestall surprises.

  1. Place 2 stacks of 2 standoffs in the standoff holes in the case. Use plastic standoffs where possible

  2. Place the DC to DC converter on the bottom of the case trying to keep the non-taped surface of the converter against the case (for heat dissipation).

  3. Place approximately 1/2" of insulating material (for example, the packing material from the VGA board works nicely) next to the DC converter.

  4. Temporarily undo the male banana jacks from the DC converter to run the power wires out of the medium-small round hole in the front of the case.
  5. Attach the clock battery to the utility connector. Duct tape the connector to make sure it stays.

  6. Attach the keyboard port to the front of the case. Place the "on" LED in one of the smallest round holes on the front of the case.
  7. Cover the pins on the bottom of the CPU board in duct tape.

    Bare pins

    Covered pins

  8. Cover the bottom and top of the disk drive (BUT NOT THE SIDES) in duct tape to insulate it.

  9. Plug the IDE cable into the CPU board, and put a right angle bend in it.

    Hook up the other end to the hard drive, and wrap the cable around the hard drive so that it will fit under the CPU board.

  10. Place the CPU and disk in the case, and screw in a third layer of standoffs to hold it in place.

  11. Attach a standoff to the hole furtherest from the front of the Private Eye driver board. Attach the driver board to the CPU module.

    (Note that in this image the Private Eye driver board 8 pin connector has already been replaced)

  12. Attach the serial, parallel, Private Eye, Keyboard, ports to the boards.

  13. Plug the Private Eye into its driver board, and test the system to make sure the machine boots.

Private Eye modification

If you've completed the above instructions, the Private eye 8 pin connector sticks out of the right hand side of the case too much.

There are several ways to handle this

  1. Cut a hole in the case to accomodate this connector (a dremel tool with cutting disk is useful for this).
  2. Buy a male to female straight through DIN 8 extender and attach the result to the front of the case
  3. Attach a new connector using the instructions below.
In general, we find the DIN 8's to be too unreliable (get bumped out). So, instead, we replace the connector on the board with a cable to a DB9 male connector that can take the place of the first serial port on the front of the case. The first port is then simply hung off the back of the machine. The Private Eye cable itself is then replaced with a female DB9 which can be screwed into the matching connector in the case. SO:

  1. Desolder the present 8 pin connector. This takes a combination of patience and ruthlessness. The main trick is not to heat up the solder joints more than necessary to remove a pin and not to slip accidentally, cutting traces on the board. First remove the DIN 8 connector's hood.

    A soldering iron and a pair of needle nose pliers can be used to push and pull the soldered tabs out (there are no connections to worried about). Once the hood is off

    the DIN-8 pins can be desoldered. The easiest (and pretty ruthless) way is to cut slowly through the plastic of the connector, cut one of the pins, grab it with needlenose pliers, and heat up the solder joint until it comes out.

  2. The solder holes can be cleaned of residual solder by using a solder sucker.

    While this helps ease the next steps, it is not necessary.

  3. Take a serial cable with a DB9 male connector on it; cut off the other, square end; separate, strip, and tin the ends of the wires.

  4. Solder the leads into the driver board according to the following table. Wire number 1 on most serial cables is a different color than the rest (e.g. red). Looking at the bottom of the Private Eye driver board (the side WITHOUT the large chip), the holes are numbered

          1234  |
          5678  |

    These tables are for our convenience; any one to one mapping will work. The mappings are for backwards compatibility with previous iterations of the driver board.

    Private Eye driver board	DB9 cable
    1		                5
    2	                        2
    3	                        1
    4		                3
    5		                8
    6		                7
    7		                6
    8		                4
    The result should look like (from the bottom of the Private Eye driver board):

  5. Cut the 8 pin connector off the end of the Private Eye.

  6. Rewire, using the following table, the Private Eye to a DB9 female connector.

    Private Eye connector	female DB9 (as labeled on the connector itself)
    yellow(1)		1
    blue  (2)		6
    green (3)		2
    white (4)		7
    brown (5)		3
    red   (6)		8
    black (7)		4
    orange(8)      		9

    Altogether, you should have something like

  7. Test the system to make sure the wire is correct.
  8. Strain relieve and properly case the connector: Partially assemble the strain guard

    and place it on the cable. Determine where it should be placed such that strain will be put on it and not on the DB9 solder joints.

    Finish assembling the strain guard and tighten in place. Note that for the thickness of the Private Eye cord, the plates of the guard have to be nested together like spoons in order to get a tight fit. The result should be tight enough that it should be almost impossible to slide the strain guard along the cord.

    Place the assembly into the DB9 case, slide the 2 fastening screws into place, and put the 2 RS232 captive screws in their positions

    Close the DB9 case.

    The captive screws enable fastening the Private Eye connector to the case.

Finishing up

Congratulations, you should now have a robust wearable computer. The next stage is making it comfortable to wear. The next section, "Customizing," describes at least one way of doing things but may also list alternatives. Please read all alternatives before trying one. The reader is encouraged to try their own solutions.

Copyright 1997, Thad Starner and MIT

Warrantee (or lack thereof)

Last modified: Sun Mar 16 21:17:47 EST 1997